feedc0de/boost_unordered
1
0
Fork 0
forked from boostorg/unordered
Code Pull Requests Activity

Update mix32_policy to use Fibonacci hashing

Browse Source
This commit is contained in:
Peter Dimov
2022-01-19 04:01:46 +02:00
parent 4c2150fb3d
commit d96d5335b4
1 changed files with 10 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
include/boost/unordered/detail/implementation.hpp
View File

@ -2041,26 +2041,21 @@ namespace boost {
template <typename Hash, typename T>
static inline SizeT apply_hash(Hash const& hf, T const& x)
{
SizeT key = hf(x);
// "Integer Hash Function", Thomas Wang, 1997
// https://gist.github.com/badboy/6267743
// http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
key = ~key + (key << 15); // key = (key << 15) - key - 1;
key = key ^ (key >> 12);
key = key + (key << 2);
key = key ^ (key >> 4);
key = key * 2057; // key = (key + (key << 3)) + (key << 11);
key = key ^ (key >> 16);
return key;
// https://en.wikipedia.org/wiki/Hash_function#Fibonacci_hashing
SizeT const m = 2654435769u; // 2^32 / phi
return hf(x) * m;
}
static inline SizeT to_bucket(SizeT bucket_count, SizeT hash, int bcount_log2)
{
BOOST_ASSERT( boost::core::has_single_bit( bucket_count ) );
BOOST_ASSERT( bucket_count == ( SizeT(1) << bcount_log2 ) );
return hash & (bucket_count - 1);
(void)bucket_count;
SizeT r = hash >> (32 - bcount_log2);
BOOST_ASSERT( r < bucket_count );
return r;
}
static inline SizeT new_bucket_count(SizeT min)